The present invention relates to a catalyst for hydrogenation, more particularly, it relates to a catalyst for the selective hydrogenation of alkynes in C4 cuts. The present invention also relates to a process for the preparation of the said catalyst, its use in the selective hydrogenation and a regeneration method of the said catalyst.
The C4 cuts produced in petrochemical industry represents a mixture of several alkanes and olefins containing 4 carbon atoms, in which 1,3-butadiene, deemed as one of the industrially valuable component, accounts to about 40-60 wt %, and the alkynes present as impurities, including methyl acetylene (MA), ethyl acetylene (EA) and vinyl acetylene (VA) etc., amounts to 0.5-2.5 wt %. Therefore, there is a need to hydrogenate alkynes in C4 cuts to obtain 1,3-butadiene in high purity that meets the requirements of polymerization.
One of the methods for removing alkynes is based on catalytically selective hydrogenation of alkynes by means of catalysts in such a way as to convert the alkynes, such as VA, EA, MA etc. into butadiene, butene and butane although the latter form is in a relatively small amount, thus making the C4 alkynes become valuable. The catalyst for hydrogenation used in such a alkyne-removing method should have high activity and selectivity and thereby can remove alkynes effectively while minimizing the 1,3-butadiene losses. In addition, it is desirable that the catalyst has a good running stability over time with low operation investment.
U.S. Pat. No. 4,101,451, filed on Jan. 19, 1977 and thereafter issued to The Dow Chemical Company, disclosed a process for improving the activity of a promoted copper catalyst suitable for selectively hydrogenating alkynes in liquid streams containing olefins. In the working examples of this parent, use was made of the catalyst in which the salts of Cu, Ni, Co, Cr, Mn or Ag were supported on the supporting material of xcex1-alumina containing Na2O.
JP57-185,228 disclosed a process for selective hydrogenation of alkyne compounds. The catalysts comprising Al2O3 as a support, and palladium and copper or palladium and silver as active components were used in its examples to hydrogenate alkynes in C4 cuts.
It appears that when the catalysts which are widely adopted in the prior art are used in the removal of alkynes from C4 cuts through selective hydrogenation, problems arise from the impossibility of selective hydrogenation in an efficient way of alkyne-enriched C4 cuts in which the alkyne content is, for example up to 2 wt % on the one hand, and unlikeliness of complete hydrogenation to obtain satisfactory removal of alkynes for example to the extent of 25 ppm, or even 15 ppm in alkyne content as required in the process specification in the art on the other hand. Therefore, it is necessary to seek for a catalyst which can remove alkynes from alkyne-enriched C4 cuts through selective hydrogenation steadily and efficiently.
Accordingly, it is an object of the present invention to provide a novel catalyst, which can be used to remove alkynes from alkyne-enriched C4 cuts through selective hydrogenation with high efficiency, good selectivity, prominent stability and a long life time.
It is another object of the present invention to provide a process for preparing a catalyst, which can be used to remove alkynes from alkyne-enriched C4 cuts through selective hydrogenation with high efficiency, good selectivity, prominent stability and a long life time.
It is still another object of the present invention to provide a use of the said catalyst in respect of removal of alkyne, from alkyne-enriched C4 cuts through selective hydrogenation.
It is yet a further object of the present invention to provide a process for regenerating the above-mentioned catalyst.
These and other objects are accomplished by providing in a surprising and unexpected manner a catalyst, comprising 1-30 wt % of copper as a first active component, 0.001-5 wt % of palladium as a second active component, 0.001-6 wt % of at least one metal selected from Ag, Pt, Pb, Mn, Co, Ni, Cr, Bi, Zr and Mo as a cocatalyst, and the balance of at least one support selected from alumina, silica and titania, all the percentage indicated hereinabove and hereinafter are calculated on the basis of total weight of the catalyst except those otherwise designated.
Preferably, the catalyst according to the present invention comprises 3-20 wt % of copper, 0.05-3 wt % of palladium, 0.01-4 wt % of at least one metal selected from Ag, Pt, Pb, Mn, Co, Ni, Cr, Bi, Zr and Mo as a cocatalyst, based on the total weight of the catalyst.
More preferably, the catalyst according to the present invention comprises 3-20 wt % of copper, 0.05-1 wt % of palladium, 0.01-1 wt % of at least one metal selected from Ag, Pt, Pb, Mn, Co, Ni, Cr, Bi, Zr and Mo as a cocatalyst, based on the total weight of the catalyst.
As a variant of the present invention, the weight ratio of Cu/Pd in the final catalyst is in the range of from 20xcx9c60.
As a variant of the present invention, the support used in the catalyst of the present invention is optionally treated with alkali metal salts, alkaline earth metal salts of mixtures thereof so as to enhance the catalyst selectivity and lower the surface acidity of the support and thereby control the polymerization of butadiene by reducing the possible buildup of polymers.
Preferably, the said alkali meal is selected from at least one of the group consisting of Li, Na, K, Rb and Cs, and the said alkaline earth metal is selected from at least one of the group consisting of Be, Mg, Ca, Sr and Ba.
More preferably, the said alkali metal is selected from at least one of the group consisting of Li, Na and K, and the said alkaline earth metal is selected from at least one of the group consisting of Dc, Mg and Ca.
Preferably, the amount of said alkali metal salts, alkaline earth metal salts or mixtures thereof expressed in terms of the elementary metal is 0.001-3 wt %, preferably 0.05-0.5 wt %, based on the total weight of the catalyst,
The catalyst according to the present invention has a specific surface area of 100-350 m2/g, as determined by means of model BC-1 surface area measuring instrument.
The catalyst according to the present invention has an average pore diameter of 30-200 xc3x85, as determined by means of Absorption Detector of the type Sorptomatic 1990 (Ex FISONS Corp.) in which N2 is used as an absorption gas.
Preferably, alumina, titania or silica in the form of bars, strips, platelets, cylindrical granulae, granular powders or spheroidal particle is used as a support in the catalyst of the present invention.
More preferably, alumina, titania or silica in the form of spheroidal particle of "PHgr"2-5 mm is preferably used as a support in the present catalyst.
The present invention further relates to the process for preparing the catalyst according to the present invention, comprising the steps of;
(1) The support-forming substance selected from at least one of alumina, silica or titania is calcined at 200-900xc2x0 C.;
(2) The support resulting from step (1) is impregnated in any order in a copper nitrate solution and a palladium nitrate, palladium chloride or palladium acetate solution to the extent that the copper content reaches 1-30 wt % and palladium content is 0.001-5 wt %, based on the total weight of the catalyst;
(3) The pH value of the palladium nitrate, palladium chloride or palladium acetate solution used in step (2) is adjusted to 3-6 with aqueous ammonia, sodium bicarbonate or sodium carbonate solutions;
(4) The support obtained from step (2) is calcined at 300-500xc2x0 C. for 4-10 hours;
(5) The support is impregnated in any order with a solution of salt of at least one metal selected from Ag, Pt Pb, Mn, Co, Ni, Cr, Bi, Zr and Mo as a cocatalyst simultaneously with or independently of the copper salt solution in step (2).
In accordance with a variant of the process according to the present invention, the said support is formed into bars, strips, platelets, cylindrical granulae, granular powders or spheroidal particles, preferably spheroidal particles.
More preferably, alumina, titania, or silica in the form of spheroidal particles of "PHgr"2-5 mm are used as a support in the process for preparation of the catalyst according to the present invention.
In accordance with a variant of the process according to the present invention, in step (1), the support-forming substance is calcined at 300-800xc2x0 C. for 1-8 hours.
In accordance with a variant of the process according to the present invention, in step (3), the pH is adjusted to 3xcx9c5 with aqueous ammonia or solutions of sodium bicarbonate or sodium carbonate.
In accordance with a variant of the process according to the present invention, the support is impregnated in any order with a solution of salt of at least one metal selected from Ag, Pt, Bi, Pb and Zr as a cocatalyst simultaneously with or independently of the copper salt solution in step (2).
In accordance with a variant of the process according to the present invention, in step (2), the support is impregnated in solutions of palladium nitrate, palladium chloride or palladium nitrate preferably after having been impregnated in the copper nitrate solution.
In accordance with a variant of the process according to the present invention, after step (1), it optionally comprises a step of impregnating the support obtained from the step (1) in the alkali or alkaline earth metal salt solution or mixtures thereof.
In accordance with a variant of the process according to the present invention, the weight ratio of Cu/Pd in the final catalyst is in the range of from 20 to 60.
It is preferred that the alkali metal salts alkaline earth metal salts or mixtures thereof expressed in terms of elementary metal accounts to 0.001-3 wt %, preferably 0.05xcx9c0.5 wt %, based on the total weight of the catalyst.
In accordance with the process according to the present invention, after having been impregnated with solutions of alkali or alkaline earth metal salt or mixtures thereof, the resulting support is dried and then calcined at 350-500xc2x0 C. for 6-10 hours.
The present invention further relates to the use of the catalyst according to the present invention in respect of the removal of alkynes from alkyne-enriched C4 cuts through selective hydrogenation, which comprises passing the C4 cuts with 0.5-2.5 wt % of alkynes and hydrogen gas into a fixed bed which is loaded with the catalyst according to the present invention, wherein the inlet temperature is within the range of from 20-50xc2x0 C., the reaction pressure ranges from 0.6-1.0 MPa, the liquid hourly space velocity (LHSV) is set at 2-60 hxe2x88x921 (vol./vol.), and the molar ratio of hydrogen to alkynes is ranging from 1-6.
According to a variant of the use of the catalysts according to the present invention, as regards the alkynes which can be removed through selective hydrogenation using the catalysts according to the present invention, mention may be made of methyl acetylene, ethyl acetylene and vinyl acetylene.
According to a variant of the use of the present catalysts, as regards the fixed bed as used, reference may be made to one-stage bed, double-stage bed or any other conventional catalyst beds in the art suitable for prolonging the catalyst life time.
By the wording xe2x80x9calkyne-enrichedxe2x80x9d throughout the whole text of the present application is meant such a content of alkyne that reaches as high as 2.5 wt % of the C4 cuts to be treated.
The present invention will be further illustrated with reference to the following examples, but these examples are not construed with limiting the present invention. The protection scope sought for by the present invention is defined by the appended claims.
Preparation of the Catalyst
The commercially available spheroidal particles of Al2O3 or TiO2 of "PHgr" 2-3 mm were calcined at 636xc2x0 C. for 6 hours, then optionally impregnated in the solution of alkali or alkaline earth metal salt. The resulting support was dried and calcined at 350xc2x0 C. for 6 hours and then, impregnated in a formulated solution of copper nitrate to the extent that the copper content is 1-30 wt %, based on the total weight of the catalyst. The resulting support was calcined at 300-600xc2x0 C. for 4-10 hours. Then the resulting support was impregnated in the formulated solutions of palladium nitrate, palladium chloride or palladium acetate of which pH had been adjusted to 3xcx9c5 with aqueous ammonia or solutions of sodium bicarbonate or sodium carbonate to the extent that the obtained product contains 0.001-5 wt % of palladium with the weight ratio of Cu/Pd in the final catalyst ranging from 20-60, based on the total weight of the catalyst. Again the support was calcined at 350xc2x0 C. for 6 hours. The support was impregnated in any order in a solution of salt of at least one metal as a cocatalyst selected from the group consisting of Ag, Pt, Pb, Mn, Co, Ni, Cr, Bi, Zn and Mo simultaneously with or independently of the above mentioned copper nitrate solution. The strength of the catalyst particles is of 0.6-1.0 MPa per particle.